a. Field of the Invention
The present invention relates to a method of manufacturing carboxylic acids or esters thereof.
B. Description of the Prior Art
As the method of manufacturing carboxylic acids or esters thereof, the art of making olefin, carbon monoxide and water or alcohol react with one another in the presence of a cobalt compound has long been known. This reaction is regarded as a reaction effected by substituting water or alcohol for hydrogen in the oxo synthesis, but, as a matter of fact, in the case of effecting this reaction under the same reaction conditions as in said oxo synthesis, the speed of reaction is low and the yield of carboxylic acid or ester thereof is no more than 40% of thereabout at the highest. Accordingly, there have hitherto been made various attempts for further improvement of said reaction. For instance, Japanese patent publication No. 12854/1966 discloses a method for increasing the yield of carboxylic ester by making hydrogen and pyridine base present in the reaction zone in addition to cobalt catalyst so as to increase the speed of reaction, and the Laid-open application No. 1362/1971 teaches a method for increasing the yield of adding lactam, nitrile, amide and the like to the reaction zone. But, in either case, the progress of reaction is rather slow, so that both methods employ a high temperature and a high pressure.
However, the high-temperature/high-pressure reaction generally has various defects such that (1) the quality of the resulting fatty acid or ester thereof is not very satisfactory, (2) the cost of equipment is increased, and (3) extra safety precaution must be taken at the time of operation. Especially in the case of manufacturing a variety of products in small quantities like the manufacture of hindered esters, because it is necessary to switch the apparatus from one product to another frequently, it is unavoidable that the high-temperature/high-pressure process is disadvantageous.
Under such circumstances, the low-pressure process has drawn public attention, and as a method in this line, there is known, for instance, the method of effecting the reaction by employing rhodium catalyst or iridium catalyst under a pressure of 20.about.50 atmospheres (cf. the Japanese patent publication NO. 19290/1973). However, inasmuch as this method employs a costly noble metal catalyst, there is little chance for its practical application on an industrial basis from the viewpoint of the quantitative recovery of catalyst and so on.